Marie-Claude Bon

Invasion of Lepidium draba (Brassicaceae) in the western United States: distributions and origins of chloroplast DNA haplotypes

Advances in phylogeography are of great value for understanding the population structure and origins of invasive genotypes. Such insights provide constructive information for current or future biological control research efforts. In this study, we investigated a highly variable chloroplast DNA (cpDNA) marker for populations of the weed Lepidium draba (Brassicaceae) in its native Eurasian and invasive US ranges. We sequenced DNA from 684 individuals from Eurasia and the US and found 41 different haplotypes. Our comparative study between the native and invasive ranges showed a 33% reduction in allelic richness (A) and a 7% reduction in haplotype diversity (h) since introduction into the US. Most genetic variation in the native range was observed within geographical regions and populations, not between regions, and this result was similar for the invasive range. Assignment tests indicated the most likely origins of many invasive haplotypes. Some of these occurred in western Europe, supporting an expanded native range that had been proposed for the species. Exact locations were identified for a diverse set of invasive haplotypes which can be used in ongoing host‐specificity tests of potential biological control agents.

Trichoderma asperellum sensu lato consists of two cryptic species

Analysis of a worldwide collection of strains of Trichoderma asperellum sensu lato using multilocus genealogies of four genomic regions (tef1, rpb2, act, ITS1, 2 and 5.8s rRNA), sequence polymorphism-derived (SPD) markers, matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) of the proteome and classical mycological techniques revealed two morphologically cryptic sister species within T. asperellum, T. asperellum, T. asperelloides sp. nov. and a third closely related but morphologically distinct species. T. yunnanense. Trichoderma asperellum and T. asperelloides have wide sympatric distribution on multiple continents; T. yunnanense is represented by a single strain from China. Several strains reported in the literature or represented in GenBank as T. asperellum are re-identified as T. asperelloides. Four molecular SPD typing patterns (I–IV) were found over a large geographic range. Patterns I–III were produced only by T. asperellum and pattern IV by T. asperelloides and T. yunnanense. Pattern I was found in North America, South America, Africa and Europe and Asia (Saudi Arabia). Pattern III was found in Africa, North America, South America and Asia, not in Europe. Pattern II was found only in Cameroon (central Africa) and Peru. Pattern IV was found in all continents. All SPD II pattern strains formed a strongly supported subclade within the T. asperellum clade in the phylogenetic tree based on rpb2 and MLS (combined multilocus sequence). The diversity of DNA sequences, SPD markers and polypeptides in T. asperellum suggests that further speciation is under way within T. asperellum. MALDI-TOF MS distinguished T. yunnanense from related taxa by UPGMA clustering, but separation between T. asperellum and T. asperelloides was less clear.

Genetic variability among Paecilomyces fumosoroseus isolates from various geographical and host insect origins based on the rDNA-ITS regions

The entomopathogenic hyphomycete Paecilomyces fumosoroseus is a promising candidate for biocontrol of economically important agricultural pests. Assessment of genetic relatedness of this species appears to be essential to gain insight into the monitoring of such biocontrol products. Intraspecific variation within the internal transcribed spacer region of the ribosomal RNA gene (rDNA-ITS) was studied in 48 isolates of P. fumosoroseus. These strains were isolated from different geographical and biological origins, more particularly from the silverleaf whitefly, Bemisia tabaci-argentifolii (Homoptera: Aleyrodidae), a major insect pest in field and greenhouse crops. PCR amplification of the ITS1–5.8S-ITS2 rDNA region followed by restriction analysis of the PCR products underlined the overall highly variable nature of this region. Digestion with the six endonucleases AluI, HaeIII, Hin6I, HpaII, NdeII, and SmaI allowed the separation of the isolates into three distinct groups. The group 1, representing 25 isolates, is composed of strains isolated only from the host B. tabaci-argentifolii. By contrast, the group 3 is more diffuse as it included strains from various insect host and geographical origins. Phylogenetic analysis of rDNA-ITS sequence data strongly supported the conclusions of the PCR-RFLP analysis and recognized three monophyletic groups within the P. fumosoroseus complex. The high level of polymorphism within the P. fumosoroseus species is discussed in the light of their biological origin.

Phylogeography of the Wheat Stem Sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae): Implications for Pest Management

The wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), is a key pest of wheat in the northern Great Plains of North America, and damage resulting from this species has recently expanded southward. Current pest management practices are inadequate and uncertainty regarding geographic origin, as well as limited data on population structure and dynamics across North America impede progress towards more informed management. We examined the genetic divergence between samples collected in North America and northeastern Asia, the assumed native range of C. cinctus using two mitochondrial regions (COI and 16S). Subsequently, we characterized the structure of genetic diversity in the main wheat producing areas in North America using a combination of mtDNA marker and microsatellites in samples collected both in wheat fields and in grasses in wildlands. The strong genetic divergence observed between North American samples and Asian congeners, in particular the synonimized C. hyalinatus, did not support the hypothesis of a recent American colonization by C. cinctus. Furthermore, the relatively high genetic diversity both with mtDNA and microsatellite markers offered additional evidence in favor of the native American origin of this pest. The genetic diversity of North American populations is structured into three genetic clusters and these are highly correlated with geography. Regarding the recent southern outbreaks in North America, the results tend to exclude the hypothesis of recent movement of damaging wheat stem sawfly populations from the northern area. The shift in host plant use by local populations appears to be the most likely scenario. Finally, the significance of these findings is discussed in the context of pest management.

Molecular Biology of Tropical Nitrogen-Fixing Trees in the Casuarinaceae Family

The Casuarinaceae family includes about eighty species of shrubs and trees belonging to four genera, namely: Allocasuarina, Casuarina, Ceuthostoma, and Gymnostoma. Casuarinaceae are primarily native to the Southern Hemisphere, mostly Australia and Indo-Pacific areas, from Malaysia to Polynesia. However, the range of distribution of some genera such as Casuarina has been extended considerably through artificial dissemination. All members of the family are characterized by highly reduced leaves and photosynthetic deciduous branchlets (Midgley et al., 1983; National Research Council, 1984).

PCR-based, rapid diagnosis of parasitism of Lygus spp. (Hemiptera: Miridae) by Peristenus relictus (Hymenoptera: Braconidae)

Abstract Several species of Lygus (Heteroptera: Miridae: Mirini) are serious crop pests in North America where their parasitism rate by native nymphal parasitoids is generally lower than in Europe. Peristenus relictus (Ruthe) (formerly P. stygicus Loan) (Hymenoptera: Braconidae: Euphorinae) is the predominant nymphal parasitoid of several Lygus spp. in the warm Mediterranean region and has been a candidate for introduction against Lygus hesperus Knight and L. lineolaris (Palisot de Beauvois) in the southern US. We report a rapid, sensitive, and specific PCR-based assay for diagnosis of P. relictus immature stages within Lygus nymphs that entails three steps: DNA extraction, PCR of the partial mitochondrial COI gene, and agarose gel electrophoresis. The PCR-based methodology is species-specific because the target DNA of other sympatric, congeneric species was not amplified with use of the primers developed for P. relictus diagnosis. The sensitivity of the PCR method, assessed through spike tests, was established by the detection of a ratio of 1:10,000 P. relictus DNA to Lygus DNA. Molecular diagnosis of parasitism of field collected nymphs is achievable in one day, eliminating the need to rear nymphs to obtain adult parasitoids for morphological identification.

The importance of cryptic species and subspecific populations in classic biological control of weeds: a North American perspective

Classical biological control of weeds depends on finding agents that are highly host-specific. This requires not only correctly understanding the identity of the target plant, sometimes to subspecific levels, in order to find suitable agents, but also identifying agents that are sufficiently specific to be safe and effective. Behavioral experiments and molecular genetic tools have revealed that some arthropod species previously thought to be polyphagous really consist of multiple cryptic species, host races or biotypes, some of which are more host-specific than others. Whereas true species are reproductively isolated, individuals from subspecific populations may potentially interbreed with those of other populations if they should encounter them. Furthermore, biotypes may consist of individuals sharing a genotype that is not fixed within a monophyletic group, and thus may not be evolutionarily stable. This raises the question of how such populations should be classified, and how to confirm the identity of live arthropods before releasing them as classical biological control agents. The existence of host races or cryptic species may greatly increase the number of prospective biological control agents available. However, it may also create new challenges for governmental regulation. These issues are discussed using pertinent examples, mainly from North America.

Populations of Bactrocera oleae (Diptera: Tephritidae) and Its Parasitoids in Himalayan Asia

Abstract Olive fruit fly, Bactrocera oleae Rossi, is a worldwide pest of olives. To discover new parasitoids for a biological control program in California, olives were collected from various locations in the Himalayan foothills (China, Nepal, India, Pakistan) as part of a comprehensive search for B. oleae throughout its range. Wild olives, Olea europaea ssp. cuspidata, were sparsely distributed and B. oleae-infested olives were scarce. Wild olives were most widespread in Pakistan where fly infestation reached 30%. Infested olives in southwestern China were rare, reaching only 5%. Flies were identified morphologically as B. oleae, the first record from China. No B. oleae were recovered from India or Nepal. Mitochondrial gene sequences from NADH dehydrogenase (ND1), cytochrome oxidase subunit 1 (COX1), and 16S rRNA were obtained from flies and compared with B. oleae sequences in GenBank. A single mitochondrial haplotype was found in Chinese flies. Chinese B. oleae represent a maternal lineage based on ND1 and COX1 that is highly divergent from other B. oleae. Phylogenetic analysis by maximum likelihood and Bayesian inference based on the concatenated dataset of B. oleae sequences with sequences of two close subcongeners, Bactrocera biguttula (Bezzi) and Bactrocera munroi White, and analysis of delineation of species boundaries using the genealogical sorting index, supported the idea that Chinese flies share recent common ancestry with B. oleae. Flies were parasitized by braconid wasps, Psyttalia ponerophaga (Silvestri) in Pakistan, and a Diachasmimorpha species in China. Our survey reinforces the possibility of finding new biocontrol agents of olive fruit fly in the Himalayan region.

Development and characterization of 11 microsatellite markers in the root-gall-forming weevil, Ceutorhynchus assimilis (Coleoptera: Curculionidae)

The host race of Ceutorhynchus assimilis Paykull, 1792 (Coleoptera: Curculionidae) that specifically develops on Lepidium draba Linné, 1753 (Brassicales: Brassicaceae), an invasive weed in North America, is being considered for use as a biocontrol agent. Above all, establishing the potential for gene flow between this host race and the other entities within C. assimilis, some of which are pests, is crucial to resolving its taxonomic status, and will ultimately determine if a biocontrol program utilizing this agent can be pursued. Among the 92 microsatellite loci isolated from the C. assimilis genome using 454 pyrosequencing, 31 were retained based upon consistent amplification. Eleven loci exhibited polymorphism in populations sampled in France and Spain. In those populations, the number of alleles per locus ranged from 1 to 7, and the observed and expected heterozygosities ranged from 0.000 to 0.870 and 0.000 to 0.777, respectively. Principal coordinates analysis clearly separated the two populations. These polymorphic loci are the first microsatellites developed in C. assimilis, and represent the most informative markers available for fine- and large-scale population-genetic studies to date.

Development of microsatellite markers for Peristenus digoneutis (Hymenoptera: Braconidae), a key natural enemy of tarnished plant bugs

The introduced European parasitoid Peristenus digoneutis is a key biocontrol agent of lygus bug pests in agricultural crops in the Northeastern USA. Changes in cultural practices and reduction of alfalfa culture have significantly reduced its abundance in its native range from historic levels. Of 48 microsatellite loci isolated from P. digoneutis genome using 454 pyrosequencing, 24 were retained based upon consistent amplification. Sixteen loci exhibited polymorphism in populations sampled in France and the USA. The number of alleles ranged from 2 to 9. The observed heterozygosity (Ho) and the expected heterozygosity (He) varied from 0.043 to 0.710 and from 0.103 to 0.728, respectively. Most loci conformed to Hardy–Weinberg equilibrium with the exclusion of five loci. These polymorphic loci will be valuable for population genetic studies and genetic conservation for P. digoneutis.